Attempt to demonstrate cell-mediated immunity against viral or tumor cell antigens in monkeys of different species infected with Herpesvirus saimiri (HSVS) and to assess the role of this response in determining the outcome of virus infection in the different hosts; determine responses of different species of primates to experimental infection by various strains of Epstein-Barr virus (EBV) and to evaluate the influence of the immune status of the animal on the development of disease processes.